Rolling mill

Rolling process

Generally, the rolling process of a single-stand twenty-high cold rolling mill can be divided into three stages: loading and threading, reversible rolling; unloading and recoiling< /p>

section. Twenty-high mills, especially Sendzimir twenty-high mills, use large tension for rolling; the rolling process starts from the steel strip after applying tension to the coiler/uncoiler before and after the rolling mill. It just started, and before that is the stage of loading materials and threading.

Loading and threading stage: Generally, a loading trolley is used to send the steel coil to the decoiler drum; a floating decoiler is often used for decoiling,

to ensure that the steel strip is always in the The central position of the rolling mill; the floating uncoiler is controlled by a universal hydraulic cylinder with a photoelectric centering device; after uncoiling, the steel strip is straightened by a straightening machine (three-roller straightening machine or five-roller straightening machine) ; Some rolling mills are equipped with hydraulic shears for cutting; the steel strip is passed over the coiler in front of the machine with an upward swinging guide plate and is directly sent to the twenty-high rolling mill; then the uncoiler continues to send the steel strip forward through the rolling mill. After arriving at the machine, the jaws of the coiler clamp the steel strip leader and wrap it around the drum for 2-3 turns before stopping the tape feeding and the tape threading is completed.

Reversible rolling stage: After the strip threading is completed, first place the upper and lower work rolls (the work rolls have been removed during strip threading), then adjust the rolling line, close the rolling mill closed door, and The front platen is pressed down, the outlet side wiper compresses the steel strip, the rolling mill process lubrication and cooling system starts supplying liquid, the rolling mill strip is pressed down, the coiler rotates to give the steel strip front tension, and the thickness gauges and speed gauges at the front and rear of the machine enter the rolling process. Line, the unit is running to start the first pass of rolling.

During the rolling process, if defects are found on the edge of the steel strip, which will affect the high-speed rolling, when the defective part passes through the roll;

The operator presses the button to input its defect position signal into the AGC system. When rolling is about to end, the rolling mill decelerates. When the tail of the steel strip reaches the position of the coiler in front of the machine, the unit stops and the first pass ends. The thickness gauge and speed gauge exit the rolling line, the rolling mill is pressed down and lifted up, the steel strip tension is released, the supply of cooling lubricant is stopped, and the pressure plate is lifted up.

During the second rolling pass, the steel strip moves in the opposite direction, and the positions of the front and rear of the machine are interchanged. After the start time of the second pass, the coiler runs in reverse direction

and sends the steel strip head in front of the machine to the reel jaws of the coiler in front of the machine. After the jaws clamp the strip head, it is coiled in front of the machine The machine rotates to wind the steel strip

on the reel for 2-3 turns; then, the rolling mill supplies cooling lubricant, the rolling mill presses down, and the transmission of the coiler before and after the machine is given

The tension gauge, thickness gauge and speed gauge before and after the machine enter the rolling line, and the unit starts the second pass of rolling.

Starting from the second pass, rolling is carried out back and forth between the coiler before and after the machine and the twenty-high rolling mill. Fully automatic control can be achieved when the rolling mill's Automatic Gauge Control (ACC) system is put into operation. When the defective part of the steel passes the roll during the rolling process, the rolling mill will automatically slow down. At the end of rolling, the rolling mill will automatically stop.

Generally, a reversible rolling mill can roll an odd number of passes, but when the coiler before and after the mill is an expansion-contraction coil, it can roll an even number of passes

, that is, when the rolling mill is uncoiled The roll can also be unloaded on one side of the machine.

Generally, before the finished product is rolled in a pass, the work roll needs to be replaced to obtain high quality and special requirements for the surface quality of the steel strip

. After the finished product pass is rolled, the rolling mill stops, is pressed down and picked up, the thickness gauge and speed gauge exit the rolling line, the rolling mill stops supplying cooling lubricant, the coiler's pressure roller is pressed down, or the unloading car is raised for use The small car seat roller resists the steel coil to prevent the steel coil from loosening and the coiler rotates to wind the entire tail of the steel strip onto the drum. At this point the reversible rolling process ends.

Unloading and rewinding stages: For expansion and contraction drum coilers, unloading is relatively simple. First, use strapping tape to tie the steel coil radially

. The unloading trolley rises to hold the steel coil. The coiler drum shrinks, the jaws open, and the steel coil is held by the unloading trolley. , the unloading trolley and the auxiliary push plate of the coiler move synchronously, and the steel coil is unloaded from the coiler. The unloading trolley continues to move and sends the steel coil to the steel coil storage table.

For coilers with solid reels at the front and rear of the rolling mill, the steel coil cannot be unloaded directly from the reel. The steel coil can only be re-coiled

to an expansion-contraction machine. The steel coil can be unloaded from the reel coiler.

When Sendzimir Twenty-High Mill and Sendew Twenty-High Mill adopt solid reel coilers, the unit is generally equipped with a recoiling mechanism to transfer the finished steel coil and solid reel together from the coiling position to the recoiling and uncoiling At position i, the steel coil is then recoiled from the uncoiler to the recoiler. Since the recoiling process is performed outside the rolling area of ??the rolling mill, recoiling and rolling can be performed at the same time without affecting each other.

Rolling process

1. Reduction system

The reduction system of the rolling mill should be based on the technical parameters of the rolling mill, the mechanical properties of the rolled materials, and the properties of the product. Quality requirements are determined

as well as high production capacity and low consumption of the rolling mill.

It is relatively easy to roll high-quality carbon steel with a twenty-high rolling mill. The purpose of using a twenty-high rolling mill is to pursue high quality

products with high The dimensional accuracy, plate shape and surface quality are improved to obtain thinner products.

For carbon steel, especially low carbon mild steel, on a twenty-high rolling mill, the total reduction rate in one rolling pass can reach more than 95%, and the pass reduction rate can reach 66%.

For the reversible cold rolling mill, since each pass is rolled on the same rolling mill, the reduction rate distribution of the passes is based on the iso-pressure rolling principle to determine the reduction schedule. Generally, the reduction rate of the first and second passes is the largest. As the rolled steel strip becomes hardened, the reduction rate of each pass gradually decreases so that the rolling pressure of each pass is roughly equal. .

In order to improve the production capacity of the rolling mill, on the premise of making full use of the main transmission power of the rolling mill and the coilers before and after the mill, the pass reduction rate should be increased as much as possible to reduce the Rolling passes. However, sometimes in order to obtain good plate shape and surface quality and reduce

the longitudinal thickness deviation of the steel strip, the number of rolling passes can also be appropriately increased. When the total reduction rate is the same, a larger rolling pass can be used. More rolling passes can slightly increase the strength of the steel strip. The reduction rate of the finished product pass has a greater impact on the plate shape, and is generally about 10%

.

2 Tension system

One of the characteristics of cold-rolled steel strip is tension rolling; without tension, cold rolling of steel strip cannot be carried out. Tension can reduce rolling pressure, improve plate shape, and stabilize the rolling process. The tension system is very important for cold rolling of steel strips.

Twenty-high rolling mills (and multi-rolling mills) using small-diameter work rolls, the technological characteristic of the rolling process is the use of large

tension rolling.

A large unit tension must be used because the material to be rolled has physical-mechanical property anisotropy, or the work roll has a small deformation arc length within a small

Skew, such that there is an uneven reduction and extension along the width of the strip. When the tension is redistributed in an area with a small reduction, the tension reaches the yield limit and it is possible to equalize the extension in the width direction of the strip.

In fact, when rolling on a multi-roller mill, the deformation of the metal is accomplished simultaneously by the pressure of the rolls and the strip tension established by the coiler

.

The unit tension used in a multi-roll mill depends on the physical-mechanical properties of the material and the degree of cold work hardening, the thickness of the strip

and its edge quality. The general unit tension is 20% to 70%.

In order to achieve the large unit tension and total tension necessary for a stable rolling process, it is required to install a coiler with

high-power transmission in the multi-roll mill. Generally, the motor power of the coiler of a twenty-high rolling mill reaches 70% to 80% of the main transmission power of the rolling mill, and some even reach 100%.

The tension of each pass is determined as follows. Generally speaking, during the first pass of rolling, since the coiling tension of the pickling unit is relatively small, in order to avoid causing the steel strip to move between layers and scratch the surface, the post-tension of the first pass is The root is small and smaller than the coiling tension of the pickling unit.

In order to increase the post-rolling tension of the first pass, a pressure plate is provided on the entrance side of the twenty-high rolling mill to increase the post-rolling tension; the front tension can be determined freely according to process requirements.

In the subsequent rolling passes, the type and specification of the rolled steel strip should be determined, or the front tension

should be greater than the rear tension, or the rear tension should be greater than the front tension.

Generally, the pre-rolling tension of the previous pass is used as the post-rolling tension of this pass. The unit front tension is greater than the unit post-tension. There are two situations for the front tension (coiling tension) of the finished product pass. For expansion-type drum coilers, since the coil can be unloaded directly on the coiler and the steel coil directly enters the bell-type furnace for tight coiling and annealing, in order to prevent bonding during annealing, the coiling tension should be reduced, and the coiling tension should be reduced. When the tension is less than 50Mpa, the probability of annealing bonding is very low, but low coiling tension will affect the production capacity of the rolling mill; for solid reel coilers, due to the need for recoiling, recoiling can

Use smaller tension (10-40Mpa), so large tension can be used during rolling, which can improve the production capacity of the rolling mill.

The tension of the pass should also be adjusted at any time according to the plate shape, especially when the rolled strip is thin. When there are waves in the middle of the material, the tension should be reduced to prevent the strip from cracking or breaking; when the strip has edge waves, the tension can be increased appropriately.

3 Speed ??System

The rolling speed should be determined according to the capacity of the equipment, and the highest rolling speed should be used as much as possible within the speed range allowed by the rolling mill

The rolling speed is increased to improve the production capacity of the rolling mill; at the same time, when the rolling speed increases, the rolling pressure decreases accordingly.

Generally, a lower rolling speed is used in the first pass of rolling, because the reduction in the first pass is large. If high-speed rolling is used again,

The rolls heat up rapidly. Due to the poor cooling conditions of the multi-roll mill, the life of the rolls will be affected. In addition, due to the large longitudinal thickness deviation of the billet, the plate shape does not completely match the rolls. The billet must be adjusted during the first rolling pass, which requires speed. Lower; while using high speed and large pressure, the capacity of the main motor cannot be satisfied.

For subsequent passes, the rolling speed is determined based on the reduction system, tension system and the power of the main motor, so that the capability of the main motor can be fully utilized.

When starting and braking each pass of rolling, there is a speed-up and speed-down process respectively. During the rolling process, the speed should be adjusted as little as possible to ensure the stability of rolling and achieve uniformity of thickness deviation.

4-roll shape

Due to the rigidity and zero-convex design of the twenty-high rolling mill frame, as well as a variety of effective adjustment methods for the roll shape,

The twenty-high rolling mill can use all flat rolls without roll crown for rolling. According to needs, the work roll and the second intermediate roll can also be appropriately configured with crown rollers; the first intermediate roll is always a flat roll, but the head has a taper for axial adjustment of the roll; support The backing bearing of the roller must not have convexity.